How to derive the radius

[regis101]

Greetings. Newbie says hello.

I saw the plans for the Benroy listed above. Very close to what I'd want. Nice to see the radius dimensions for the front and ear. This is info that I was looking for to understand how peoples come up with their individual design.

My point of this thread is to ask how some of you derived your radius and what tasty beverage helped you to get there .j/k

I am partial to the golden rule of measurement stemming form my old woodshop speaker box building daze. The basic rule is 1 : 1.618 : .6 where the 1 = w, 1.618 = l, and .6 = d.

With regards to the side profile using the Benroy plan, with a front radius of 19, the rear radius would be 30.7 This method wouldn't have the classic teardrop rear sweep but could be used as a baseline.

I really like the profile from the top of page two of the side profile sticky. It was tears&sweat's first build . Trying to figure out his radii. Yes radii is a word.

Just some thoughts. Again, newbie says hello.

[mikeschn]

Hi Regis,

Originally the Benroy didn't have a radius on the rear. It was an elliptical curve. But who is going to build a benroy with an elliptical curve? So I simplified it with two radii.

As for what I was drinking when I developed it, probably wine!!!

Mike...

[regis101]

Awesome plans, by the way.

I just spent some time in the garage laying out a side profile with three rear curves and keeping an 18" r front. Of the three, I like the line from 6" up from the bottom and letting it land where it may on the top using a 48"r. That works out at about the 40" mark. This coincides with the ~60/40 split of the trailers wheels. All things for a reason. Yes, I know. Thinking too much. But who doesn't.

[regis101]

This what my half of the garage floor looks like. Based on 4 x 8

[caseydog]

But who is going to build a benroy with an elliptical curve?

I used an elliptical curve for my rear curve.

CD

[regis101]

Cool.

I will build one of these soon. It is going to be mainly a cargo hauler for our camping gear. But has to have a little something something instead of just a box. I may end up with smaller rear radius just to take advantage of some cu ft. I like the 18"r front.

We use a VW camper van so weight or less of it is important. Just need a trailer to haul the stuff instead of jamming it all into the Buses cabin. Poor dog party's at the kennel a lot since there is not room for her.

I'll build it as a skid so it's removeable from the trailer. There all just plans now. But it'll happen.

[Dean in Eureka, CA]

This is a good page to check out...
Andrew's Foci Page
An easy formula I use that I got from Andrew is...
Foci equals the square root of A squared minus B squared. (A being major radius and B being minor radius of the ellipse)
Just be sure to put both Focus points along the major axis on each side of the minor axis... Just like Andrew shows on his page. The formula was on that page at one time, but he must've removed it...

[wannabefree]

Wow. What's a foci?

I took a sheet of plywood, made a spline (a long thin piece of wood), laid it on the plywood and bent it until I liked the profile. No math. No measurements. No pain.

[tonyj]

Hi Regis,

But who is going to build a benroy with an elliptical curve?

Mike...

Uhhh . . . . . Me?

[kennyrayandersen]

Wow. What's a foci?

I took a sheet of plywood, made a spline (a long thin piece of wood), laid it on the plywood and bent it until I liked the profile. No math. No measurements. No pain.

It's a delicacy in some Asian countries!
Just trace it from the blocks or use the string method described in the library. In my opinion the ellipse changes the Benroy into a tear fro.... OK, I won't go there -- too many Benroy owners on board Anyway -- thumbs up on the ellipse

[Alfred]

You should never drink and derive at the same time! You might get arrested for deriving while intoxicated!

(Doh!)

Al in Asheville

[angib]

Yep, if you want to calculate the position of the focuses, Dean has it right.

a^2 = b^2 + c^2

(or in English, a-squared = b-squared + c-squared)

where c is the distance from the centre to the focus.



Andrew